fixed a potential invalid read/write error, access to object and its potential destruction was done in wrong order

Supports specifying modules in xml config.

the swicth because order is not important for these.

ModuleList serves as a container for VariableGroups. The VariableGroups
mirror xml modules in the config file.

Xml parsing logic factored out to class ConfigParser.

 - Have a ZMQ push-type variable from a DOOCS-backed device that is NOT
   used as a trigger (otherwise the bug does not happen)
 - Connect that to an ScalarPushInput in an ApplicationModule
 - call readAnyGroup() from the ApplicationModule's main method

=> ReadAnyGroup.finalise() will cause an infinite recursion between
ExceptionHandlingDecorator::doReadTransferAsync and
TransferElement::readAsync because of wrong dispatching to the decorated
type

- Make doxygen pick up markdown.
- introduced: set_default_build_to_release.cmake

set_default_build_type_to_release.cmake -> set_default_build_to_release.cmake

- add test for full exception handling

  DeviceModule and ControlSystemModule now do not take the optional prefix argument in their constructors any more. Use the [] operator instead to get the submodule.

- Add ExceptionHandlingDecorator and decorate all device variables with it.

move ApplicationModule::appConfig() to ModuleImpl::appConfig() so it can also be used from ModuleGroup

'*.md' files put into the projects doc directory will be picked as part of
the documentation. '*.md' files in other locations of the source tree will
be ignored.

add ConfigReader.h to ApplicationCore.h, as the ConfigReader is now more strongly integrated with ApplicationCore